There are known isolated switching power sources, an example of which is disclosed in Japanese Patent Application Publication No. 2011-244619. An isolated switching power source disclosed in the Patent Publication is comprised of a transformer that partitions the circuit region of the isolated switching power source into an input circuit region in which a power source lies and an output circuit region while the input circuit region is electrically isolated from the output circuit region. The isolated switching power source is designed to transfer power output from the power source to the output circuit region. Specifically, in addition to the transformer, the isolated switching power source is comprised of a control circuit designed specifically therefor. The control circuit performs feedback control of an output value, such as an output current value from the isolated switching power source, which adjusts the output value to a target value.